Project Summary: This proposal addresses a knowledge gap concerning the causes of postoperative hip dislocation, a condition with associated annual costs exceeding ~$500 million in the U.S. Hip dislocation occurs when the femoral head is forced out of its acetabular socket. Dislocation of a prosthetic femoral head following total hip arthroplasty is thought to occur when the maximum prosthetic range of motion is less than the functional range of hip motion required to perform daily activities. In particular, non-optimal acetabular and femoral component orientation (e.g., abduction and anteversion), which are unique for each patient, can cause such a mismatch. The acetabular and femoral orientations vary with natural 3D pelvic tilting during activities of daily living that require tilting. The pelvic tilt itself can also change over time with the progression of degenerative disc disease or because of spinal surgeries. The pelvic tilt has received little attention in the literature. Currently, both conventional and computer-assisted total hip arthroplasty are guided by the concept of a 2-dimensional (2D) safe zone for acetabular implant anteversion; this 2D safe zone was developed in 1978 and requires updating. My working hypothesis is that pelvic tilt in all three cardinal planes during daily activities is one of the major factors that affects hip dislocation rate. Thus, PI Dr. Eslam Pour is proposing to develop a new personalized surgical planning tool for orthopedic surgeons that will establish optimal implant component orientations for each total hip arthroplasty patient. The planning tool will be customized for the range of 3D pelvic tilts measured using either regular lateral lumbar radiographs or the EOS system in three common activities of daily living: standing, sitting and moving from sitting-to-standing. In Aim 1, a 3D computer model will be developed to predict the optimal implant anteversion and abduction for any given values of 3D pelvic tilt and the required range of motion in different daily activities. In Aim 2, the new safe zone created by the 3D computer model from Aim 1 will be validated retrospectively using collected images from patients who had pre- and postoperative EOS imaging during their total hip arthroplasty process. Once validated, the new tool can be used for pre-operative total hip arthroplasty surgical planning to reduce the risk for prosthetic dislocation. We will then apply for an R01 to test this new 3D safe zone model in a multicenter study. Dr. Eslam Pour has assembled a highly experienced, multidisciplinary mentorship team in a strong research environment. He will leverage these excellent resources to address his educational needs and career goals by following the detailed educational and mentorship included in this proposal. Together, the training and research supported by this proposal will propel him to become a successful independent investigator and a national leader in hip arthroplasty research.